1. Field of the Invention
The present invention relates to an electronic photosensitive body having a photoconductive layer including a non-single crystal material of which the main body is silicon, and a manufacturing method for the same, as well as an image forming apparatus.
2. Description of Related Art
Methods for forming an image on a recording medium, such as paper, include electronic photography systems. In electronic photography systems, an image is formed on a recording medium by repeatedly carrying out charging, exposure to light, development, transcription and static elimination on a photosensitive body. Electronic photography systems are adopted in copiers and printers. Bases where a photosensitive layer is formed on the surface are used as photosensitive bodies. Photoconductive layers made of amorphous silicon are adopted as photosensitive layers.
During image formation in electronic photography systems, in some cases there is light memory, so that an afterimage generated by exposure to light in a previous copying step affects the following copying step (ghost). Light memory is considered to be generated when photo carriers generated in portions irradiated with intense light during exposure to light are trapped in the photosensitive layer in such a manner as to affect the following charge. In addition, in some cases there is light memory when a portion that is not irradiated with intense light during exposure to light is irradiated with light for static elimination in order to remove the charge. That is to say, in some cases photo carriers generated by light for static elimination, in addition to light for exposure, are trapped in the photosensitive layer, and thus affect the following charge. In particular, irradiation with intense light for static elimination for reducing the effects of light memory during exposure to light makes the effects more significant.
In general a region where absorption changes exponentially for a change in energy can be observed on the low energy side, starting from the absorption end in light absorption spectra of amorphous semiconductors. This region is referred to as exponential tail (Urbach's tail). In this region, the following Formula 1 holds between the optical absorption coefficient α and the photon energy hω of incident light. Here, E in Formula 1 is referred to as characteristic energy.α=C·exp(hω/E)  [Formula 1]
C: constant
hω: photon energy
h: rationalized Planck constant
ω: frequency
The following Formula 2 can be made using the logarithm on both sides in Formula 1.ln α=(1/E)·hω+ln C  [Formula 2]
The inverse number of the characteristic energy E (1/E) corresponds to the inclination when the logarithm (ln α) of the light absorption constant α is taken along the longitudinal axis and the photon energy (hω) is taken along the lateral axis. The light absorption spectrum is approximately linear in the exponential tail region. The size of the characteristic energy E in this linear region is mutually related to the amount of carriers captured by the band tail. When the characteristic energy E is small (1/E is large), for example, less carriers are captured by the band tail, and thus, memory can be reduced during exposure to light (see for example Patent Documents 1 and 2).
Patent Document 1 discloses an electronic photography system where the memory can be reduced by keeping the characteristic energy in the photoconductive layer 0.09 eV or less. Patent Document 2 discloses a photoconductive layer, which is formed of a first layer having a characteristic energy E of 50 meV to 65 meV and a second layer having a characteristic energy E of 50 meV to 55 meV, and thus has little memory.
To be sure it is effective to expose a film having little characteristic energy E with an appropriate amount of light in order to reduce memory during exposure to light and static elimination. However, it is necessary for the rate of film formation to be low, or for the gas flow to be large, in order to make the characteristic energy E in the photoconductive layer small, and in either case, a problem arises in terms of the cost of manufacture.    Patent Document 1: Japanese Unexamined Patent Publication S62 (1987)-83470    Patent Document 2: Japanese Patent No. 3754751